MELEXIS EVB90401A

EVB90401
MLX90401 Demo Board
Introduction
The MLX90401 Demo Board described in this
document is designed to show the operation
and performance of the Brushless DC Motor
Controller and to simplify the design of new
applications.
The Demo Board provides the necessary
external components to facilitate evaluation of
the MLX90401 without having to design and
construct external circuitry. Several control
switches and a potentiometer are available on
the Board. A regulated DC power supply is the
only input signal.
A brushless DC motor with Hall effect sensors
is NOT included with the Demo Board, but any
can be used.
Ordering Information
Part No.
EVB90401A
EVB90401B
390119040101
Rev 002
Power supply range of target application
12V to 24V
20V to 40V
Page 1 of 6
Application Note
15-Jul-05
EVB90401
MLX90401 Demo Board
1 Demo Board description
1.1 Schematic
SW1
ON/OFF
V+
0
Vref
HA
HB
HC
0
R1
(see
text)
R2
1k5
DZ1
15V
C1
330u/
63V
IC1
MLX90401
C2
100n
1
Supply Voltage
Cap Boost "A"
24
2
VREF Out
Gate Top "A"
23
Hall "A" Input
Feedback "A"
22
4
Hall "B" Input
Cap Boost "B"
21
5
Hall "C" Input
Gate Top "B"
20
6
Fwd/Rev Input
Feedback "B"
19
7
Speed Adjust
Input / Disable
Cap Boost "C"
18
8
Oscillator R/C
Gate Top "C"
17
D3
D2
LED
VREF
3
C4
22u/
25V
ROSC
10k
P1
100k
C5
100n
R4
1k
Speed
COSC
5nF
Fw/Rev
C7
10n
R6
C8
10n
R7
C9
10n
Q1
D4
D6
M1
M2
M3
Q2
D5
9
/Brake Input
Feedback "C"
16
10
Analog Ground
Gate Bottom
"A"
15
11
60°/120°
Select Input
Gate Bottom
"B"
14
12
Power Ground
Gate Bottom
"C"
13
TP2
Disable
R5
R8
D7
Q3
Q4
R9
R10
TP1
Brake
D8
Q5
Q6
R5 ... R10 = 22R
Q1 ... Q6 = IRF530
D3 ... D5 = 1N4148
D6 … D8 = 1N4007
60/120
1.2 Board layout
The following diagram shows a schematic overview of the most important parts of the Demo Board:
MLX90401 Demo Board
OFF ON
V+
0
M1 M2 M3
Vref HA HB HC
MLX
90401
pin1
0
Speed adjust
390119040101
Rev 002
Disable
Brake
60/120
Fw/Rev
Page 2 of 6
Disable
Brake
Application Note
15-Jul-05
EVB90401
MLX90401 Demo Board
1.3 Functional Description
The Demo Board mainly consists of the following blocks:
•
15V regulator with an On/Off switch and a power-on indication LED
•
Connectors for power supply, Hall effect sensors and brushless DC motor
•
Three push button switches for controlling the motor: Brake, Forward/Reverse (Fw/Rev) and
Disable
•
One push button switch for setting 60° or 120° sensor electrical phasing of the motor (60/120)
•
A potentiometer to control motor speed (Speed adjust)
•
1 on-board MLX90401 Brushless DC Motor Controller
•
External components for oscillator, charge boost and protection.
The main purpose of the board is to demonstrate the functionality and capabilities of the MLX90401.
With a power supply and a brushless DC motor connected, the buttons and potentiometer can be used to
fully control the motor.
An on-board zener diode regulator provides a voltage of 15V for the chip. That way the external power
supply – which is also supplied to the motor - can be as high as 40V. R1 (and if necessary also the zener
diode) can be optimized for a specific power supply voltage (see Remarks below). Two versions of the
Demo Board can be ordered, each for a specific power supply voltage range. (See Order Information for
more details.)
The Vref pin (output of the MLX90401) serves as a 12V supply for the Hall effect sensors.
The Disable input can be used for protection purposes. Pulling the Disable input low turns off all drivers.
When the motor is disabled in such a way, it will come to a standstill due to friction. No active braking is
applied.
Any sort of switch can be used to pull the Disable input low.
An option is the use of a thermal switch. This thermal switch can be used to monitor the temperature of
the drivers MOSFETs. If the MOSFETs get too hot, the thermal switch will pull the Disable input low.
R3
10k
P1
100k
R4
1k
Speed
C6
100n
C3
4n7
Fw/Rev
6
Fwd/Rev Input
Feedback "B"
19
7
Speed Adjust
Input / Disable
Cap Boost "C"
18
8
Oscillator R/C
Gate Top "C"
17
9
/Brake Input
Feedback "C"
16
10
Analog Ground
Gate Bottom
"A"
15
11
60°/120°
Select Input
Gate Bottom
"B"
14
12
Power Ground
Gate Bottom
"C"
13
Q3
Q4
Q5
Q6
Brake
60/120
°T
Disable
Thermally
linked
Another possibility is the use of a Hall effect switch. When the current through the driver MOSFETs
reaches a certain threshold, the magnetic field induced in the sense coil will exceed the Hall effect switch
threshold. The Hall effect switch should then switch to the “ON” state, and in that way pull the Disable
input low. This in turn switches off all drivers.
390119040101
Rev 002
Page 3 of 6
Application Note
15-Jul-05
EVB90401
MLX90401 Demo Board
R3
10k
P1
100k
R4
1k
Speed
C6
100n
C3
4n7
Fw/Rev
6
Fwd/Rev Input
Feedback "B"
19
7
Speed Adjust
Input / Disable
Cap Boost "C"
18
8
Oscillator R/C
Gate Top "C"
17
9
/Brake Input
Feedback "C"
16
10
Analog Ground
Gate Bottom
"A"
15
11
60°/120°
Select Input
Gate Bottom
"B"
14
12
Power Ground
Gate Bottom
"C"
13
Q3
Q4
Q5
Q6
Brake
60/120
Disable
Hall switch
e.g.
US5881
L1
Also, a sense resistor can be used to measure the current through the motor. The current will produce a
voltage drop across the sense resistor. This voltage, amplified and filtered, can be compared with a
reference voltage. If the voltage (proportional to the current) exceeds the reference voltage, the Disable
pin is pulled low and drivers are switched off.
ROSC
10k
P1
100k
R4
1k
Speed
C6
100n
COSC
5nF
Fw/Rev
6
Fwd/Rev Input
Feedback "B"
19
7
Speed Adjust
Input / Disable
Cap Boost "C"
18
8
Oscillator R/C
Gate Top "C"
17
9
/Brake Input
Feedback "C"
16
10
Analog Ground
Gate Bottom
"A"
15
11
60°/120°
Select Input
Gate Bottom
"B"
14
12
Power Ground
Gate Bottom
"C"
13
Q3
Q4
Q5
Q6
Brake
60/120
+
FILTER
COMP
A
RSENSE
VREF
A Test Pin is available on the Demo Board as a connection point for the Disable signal.
A Test Pin is also available on the Brake signal.
1.4 Bill of Materials for the Demo
•
•
•
•
A Demo Board with on-board MLX90401
A regulated power supply (laboratory power supply, battery etc.)
A brushless DC motor
(Oscilloscope)
390119040101
Rev 002
Page 4 of 6
Application Note
15-Jul-05
EVB90401
MLX90401 Demo Board
1.5 Operation
To operate the Demo Board the following steps are necessary:
•
Connect the motor windings and Hall effect sensors.
•
Select 60° or 120° sensor electrical phasing depending on the motor used, with the push button
switch 60/120.
•
Connect the power supply.
•
Use the push button switches and potentiometer to control the motor.
2 Remarks
2.1 Using standard power supplies
When using normal power supplies that are normally found in laboratories, there is one thing to keep in
mind. Most of these power supplies cannot sink current. When an electrical motor is braked it acts as a
generator. This causes reverse currents to flow out of the motor. This energy cannot be absorbed by the
power supply, and the supply voltage can be raised by a large degree. The supply voltage may even go
higher than the breakdown voltage of certain components, including the MLX90401, and by doing
so destroy the circuit.
The solution for this issue is the following:
•
Connect a high-power zener diode (5 Watt) across the power supply, with a zener voltage of a
few volts above the normal operating supply voltage.
•
This zener diode will start to conduct if the supply voltage is raised above its zener voltage by the
motor. That way a path is created for the excessive current to flow.
•
The supply voltage will also be limited to the zener voltage.
When a battery (e.g. a 12V car battery) is used, this problem does not occur, since the battery can absorb
the fly back energy from the motor with significantly raising the battery voltage.
2.2 Power off
When the board is powered off (e.g. using the On/Off switch) the MLX90401 is no longer powered.
However as in many applications the motor is still rotating after power off the motor generates a voltage
that is not clamped or limited. If this voltage exceeds the maximum voltage rating the MLX90401
could be destroyed.
The solution is either:
•
To disable or brake the motor until standstill before powering off the board or application.
•
Or to solder a power zener diode behind the switch between supply and ground that can drain the
motor fly back power after opening the switch. Mind that zener diode DZ1 is not suitable to drain
the motor power.
390119040101
Rev 002
Page 5 of 6
Application Note
15-Jul-05
EVB90401
MLX90401 Demo Board
2.3 Optimum value of R1
The minimum value of resistor R1 is determined by the minimum power supply voltage available for the
chip. VCHIP,MIN should be at least 8V (undervoltage VUV) for the drivers to work.
VCHIP,MIN = VSUPPLY,MIN – R1 x ICHIP
For example:
VCHIP,MIN = 24V – 220R x 35mA = 16.3V
The maximum value of the resistor determines the power dissipation of the resistor:
PR1 = (VSUPPLY – VCHIP) x ICHIP
For example:
PR1 = (24V – 15V) x 35mA = 315mW
For instance, if a standard 12V battery is used, make R1=100R.
VCHIP = 12V – 100R x 35mA = 8.5V > VUV = 8V
PR1 = (12V – 8.5V) x 35mA = 122.5mW
VSUPPLY
VCHIP
R1
PR1
(V)
(V)
(Ohm)
(W)
> 23.0
15
220
> 0.37
16.0
8.3
220
0.27
12.0
8.5
100
0.13
8.0
8.0
0
0.00
Table 1: Recommended value of R1 in function of supply voltage
(with DZ1 = 15V zener diode)
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Phone: +32 1367 0495
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390119040101
Rev 002
Page 6 of 6
Application Note
15-Jul-05